Effect of carbon fiber and thermoplastic resin on laminates under lightning and dielectric strength tests

The incorporation of carbon fiber (CF) and thermoplastic resin in wind turbine rotor-blade represents a challenge for lightning events because CF conducts electricity and the behavior of thermoplastic resins is not well known. A comparative study with laminates with epoxy or thermoplastic resins was performed, using lightning and dielectric strength tests. Lightning tests revealed that resins behaved similarly; the current preferentially flowed in fiber direction and in zones with high contact between fibers (e.g., criss-crossed fibers at panel edges); the level of through-thickness damage was inversely related to panel thickness; current flow did not affect the tensile properties in fiber direction, but produced a drop in bending strength; the adequate integration of earth terminals in CF laminates was critical for a proper lightning discharge. In dielectric tests, it was concluded that panels with glass fiber covering CF laminates behaved as through-thickness insulators; the thermoplastic reduced the laminate's dielectric strength, while the incorporation of CF, or laminate aging in a salt spray chamber showed no difference. Electrical resistance tests showed that the results were not dependent on the type of resin, but on the level of fiber-to-fiber and fiber-to-terminal contact. The lowest linear resistance was obtained in the longitudinal fiber direction, followed by the transverse and through-thickness ones.

Automated summary

The challenge of incorporating carbon fiber and thermoplastic resin in wind turbine rotor-blades lies in their behavior during lightning events. A comparative study using lightning and dielectric strength tests was conducted, revealing that the behavior of the resins was similar. The integration of earth terminals in carbon fiber laminates was crucial for proper lightning discharge, and the fiber-to-fiber and fiber-to-terminal contact affected the electrical resistance of the laminates.